The present invention relates to an air conditioner, or more in particular to an air conditioner which is capable of removing the frost attached to an outdoor heat exchanger in a heating mode.
A method of removing the frost attached to the surface of an outdoor heat exchanger during the heating operation of an air conditioner of the heat pump type is disclosed, for example, in JP-A-59-208340 for which an application was filed by Toshiba Corporation on May 13, 1983. According to this method, the refrigerant that has exchanged heat with the indoor air in an indoor heat exchanger in the heating mode is applied directly to an outdoor heat exchanger without being reduced in pressure by a capillary tube. The refrigerant that has bypassed the capillary tube is kept at a comparatively high temperature, and therefore, if the fan of the outdoor heat exchanger is stopped, is capable of heating the outdoor heat exchanger, thereby promoting the defrosting effect. In this method, which utilizes for defrosting operation what may be considered the residual heat of the refrigerant that has completed heat exchange in the indoor heat exchanger, the reduced quantity of heat of the refrigerant results in a comparatively long time required for defrosting in spite of the advantage that the defrosting operation is possible while the room is being heated.
Another example of the defrosting method is disclosed in JP-A-61-175430 for which an application was filed by Tohoku Electric Power Co., Inc. on Jan. 31, 1985. According to one method described therein, all of the high-temperature high-pressure refrigerant compressed by a compressor is supplied directly to an outdoor heat exchanger. In this method, despite the high defrosting speed, the fact that the refrigerant deprived of heat by defrosting operation of the outdoor heat exchanger is applied through an indoor heat exchanger causes a great reduction in room temperature during the defrosting operation. If the conditioner is set in heating mode after defrosting, therefore, large power and long time are required until the room temperature is increased sufficiently. According to another method disclosed in the same patent application, a high-temperature high-pressure refrigerant from a compressor is supplied to an indoor heat exchanger on one hand, and partly applied to an outdoor heat exchanger for the purpose of defrosting on the other hand. This method is liable to cause a shortage of the quantity of heat for defrosting in the case where the atmospheric temperature is low.